title: The ductal origin of structural and functional heterogeneity between pancreatic islets.
abstract: Islets form in the pancreas after the first endocrine cells have arisen as either single cells or small cell clusters in the epithelial cords. These cords constitute the developing pancreas in one of its earliest recognizable stages. Islet formation begins at the time the cords transform into a branching ductal system, continues while the ductal system expands, and finally stops before the exocrine tissue of ducts and acini reaches its final expansion. Thus, islets continuously arise from founder cells located in the branching and ramifying ducts. Islets arising from proximal duct cells locate between the exocrine lobules, develop strong autonomic and sensory innervations, and pass their blood to efferent veins (insulo-venous efferent system). Islets arising from cells of more distal ducts locate within the exocrine lobules, respond to nerve impulses ending at neighbouring blood vessels, and pass their blood to the surrounding acini (insulo-acinar portal system). Consequently, the section of the ductal system from which an islet arises determines to a large extent its future neighbouring tissue, architecture, properties, and functions. We note that islets interlobular in position are frequently found in rodents (rats and mice), whereas intralobularly-located, peripheral duct islets prevail in humans and cattle. Also, we expound on bovine foetal Laguesse islets as a prominent foetal type of type 1 interlobular neuro-insular complexes, similar to neuro-insular associations frequently found in rodents. Finally, we consider the probable physiological and pathophysiological implications of the different islet positions within and between species.
authors.affiliation: Institute of Anatomy, Faculty of Medicine, University of Leipzig, Liebigstraße 13, 04103 Leipzig, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Merkwitz
authors.forename: Orest W
authors.initials: OW
authors.lastname: Blaschuk
authors.forename: Angela
authors.initials: A
authors.lastname: Schulz
authors.forename: Paul
authors.initials: P
authors.lastname: Lochhead
authors.forename: Jaroslawna
authors.initials: J
authors.lastname: Meister
authors.forename: Angela
authors.initials: A
authors.lastname: Ehrlich
authors.forename: Albert M
authors.initials: AM
authors.lastname: Ricken
mesh_terms: D000818:Animals; D002417:Cattle; D006801:Humans; D007515:Islets of Langerhans / Q000166:cytology / Q000196:embryology* / Q000254:growth & development*; D051379:Mice; D008954:Models, Biological; D009024:Morphogenesis; D010183:Pancreatic Ducts / Q000166:cytology / Q000196:embryology* / Q000254:growth & development*; D051381:Rats; D013045:Species Specificity
keywords: CK; E-cadherin; EP-CAM; GCG; GHRL; GLP-1; HE; HNF1β; INS; N-CAM; N-cadherin; NGN-3; NIC; PC; PDX-1; PHHI; PPY; R-cadherin; SOX9; SRY (sex-determining region Y)-box 9; SST; T1D; TGF-β; cytokeratin; ed; embryonic day; embryonic week; epithelial cell adhesion molecule; epithelial-cadherin; ew; ghrelin; glucagon; glucagon-like peptide-1; haematoxylin and eosin; hepatocyte nuclear factor 1 beta; insulin; neural cell adhesion molecule; neural-cadherin; neuro-insular complex; neurogenin-3; pancreatic and duodenal homeobox-1; pancreatic polypeptide; pcd; persistent hyperinsulinaemic hypoglycaemia of infancy; post coitum day; postpartum; pp; prohormone convertase; retinal-cadherin; somatostatin; transforming growth factor-ß; type 1 diabetes